Heart bypass graft. Computer artwork of a heart that has had a blockage of the coronary arteries treated by coronary artery bypass graft (CABG) surgery. The coronary arteries are the small blood vessels seen running over the outer surface of the heart. They supply oxygenated blood to keep the heart muscle pumping, and a blockage can cause a fatal heart attack. The solution is to harvest arteries from elsewhere in the body and use them to bypass the blockage. One graft is seen running from the aorta, the main body artery, back to the coronary arteries.